Process for the treatment of light petroleum distillate containing undesirable sulphur compounds



Jan. 16,

1945. F A AP PROCESS FOR THE TREATMNT. OF LIGHT PETROLEUM DISTILLATE GAR 2,367,178

GONTAINING UNDESIRABLE SULPHUR COMPOUNDS Filed May 12. 1943 A TTORNEYS Patented Jan. 1945 l PROCESS FOR THE TREATMENT OF LIGHT PETROLEUM DISTILLATE CONTAINING vUNDESIRABLE SULPHUR COMPOUNDS Frank A. Apgar, Chicago, lll., assigner to Sinclair I Refining Company, New York, N. Y., a corporation of Maine Application May 12, 1943, Serial No. 486,662

9 Claims.

This invention relates to the rening of petroleum oils and more particularly to an improved process for the refining of petroleum distillates such as gasoline containing undesirable sulphur compounds, for example mercaptans.

The presence of mercaptans in gasoline was early recognized as objectionable because of their offensive odor and corrosive nature. Petroleum distillates containing such objectionable sulphur compounds are known as sour distillates and the process of freeing sour distillates of these sulphur compounds is known as sweetening The sweetening of these sour petroleum distillates has been the object of a multitude of proposed processes.

For many years, the so-called doctor treatment has been generally regarded as the most efficient method of sweetening such distillates. In the conventional doctor treatment, the sour distillate is subjected to prolonged intimate contact with an aqueous solution of caustic soda and litharge (sodium plumbite), so-called doctor solution, at or near atmospheric temperature. A typical doctor solution is one produced by admixing 125 pounds of caustic soda, '70 pounds of litharge and 125 gallons of water, The amount of this solution added to the oil is usually predetermined by tests in which additional doses are added to a sample of the distillate until it does not further darken. Almost invariably elemental sulphur is finally added to the distillate to complete the doctor break. Care is taken to avoid adding excess sulphur as the presence of sulphur renders the,

finished distillate corrosive. f

Though the doctor treatment is generally effective in sweetening sour distillates, it hasbeen found to have'disadvantages with respect to the refining of modern gasoline motor fuels. Speciiically, gasoline so sweetened has been found to be impaired as to itsanti-knock properties, as to its susceptibility to improvement of its anti-knock values by the addition of tetraethyl lead, hereinafter referred to as T. E. L., and as to its susceptibility to the action of oxidation inhibitors of the type frequently added to improve stability in storage. Particularly in present-dayl motor fuel. anti-knock properties and susceptibility to improvement thereof by the'addition of T. E. L., are of major 'importance' and it is an object of the present invention to provide Ia process* whereby one may economically effect the sweetening of the gasoline without impairment thereof.A This object and other advantages, as subsequently appear herein, are attained by my improved process.

'I'he process of my present inventionconsists primarily of two major steps. In the first; stage of the treatment, the Adistillate is brought, into intimate contact with an aqueous solution of caustic soda at an elevated temperature and with rigid exclusion of air or other oxygen-containing gases. In the second stage, the distillate from the first stage, which has been separated from the major portion of the fouled caustic solution, is intimately contacted with a suspension of lead sulphide in caustic solution, also at an elevated temperature but in the presence of controlled amounts of added air.

Advantageously, the caustic-lead sulphide suspension used in the second stage of my process may, for instance, be -supplied initially from an operation in which a sour distillate is treated at an elevated temperature with conventional doctor solution and whereby lead sulphide and lead mercaptides such as Pb(RS) 2 are formed and separated from the treated distillate with the v fouled doctor solution. In such treatment reactions occur which may be represented generally by the following equations:

where R represents a hydrocarbon radical.

The spent doctor solution separatedffrom the distillate and carrying with it the major portion of the lead mercaptides formed by the Reaction 1 and a portion of the lead sulphide formed by the Reaction 2 has been found to be a particularly convenient and advantageous source of the initial supply of the caustic-lead sulphide suspension for the second stage of my process.

The reactions occurring in the first stage of my improved process may be summarized as follows:

R representing any hydrocarbon radical.

The mercaptides formed by the Reaction A remain largely with the foul caustic solution and are hydrolyzed in the conventional regenerating system to which the separated foul caustic solution iswith advantage passed. However, a portion of these mercaptides remain in the partially sweetened distillate and pass therewith to the second stage treatment. The organic sulphides formed by the Reaction B remain in the distillate but have no greater suppressing eflect on octane characteristicsV of the distillate than the mercaptans from which they were derived.

` The primary reactions of the second stage of my process may be summarized by the following equation:

The lead sulphide appears to act as a catalyst for the Reaction C. When this lead sulphide is supplied together with lead mercaptides from the source previously suggested, the lead of the lead mercaptides present is oxidized to PbO as indicated bythe reaction and this lead oxide may be converted to lead sulphide by treatment with hydrogen sulphide. Similarly, any lead mercaptides formed during the treatment may be converted to PbS.

In order to effect the reactions within a reasonable-period of time, it is necessary to maintain the temperature of each stage of the treatment within a range of about 180 F. to about 260 F.

It is recognized that it has previously been proposed to wash sour distillate with caustic solution for the elimination of hydrogen sulphide and the like preliminary to the sweetening of the distillate with respect to organic sulphur such as mercaptides. Also, it has been proposed to sweeten sour distillate by treatment with strong caustic solution at an elevated temperatureeither preceding or following an acid treatment. Likewise the treatment of raw source distillate with finely-divided lead sulphide suspended in a caustic solution in the presence of air has previously been proposed. However, so far as I am aware, such treatment has not resulted in an economically practical process whereby the desired sweetening of the distillate is obtained without deleteriously affecting the distillate with respect to the other desirable characteristics such as previously noted herein.

The process of -my present invention is distinguished from such previously proposed operations by a sequence of correlated steps carried out under the hereindescribed conditions. The desired sweetening of the distillate in conjunction with the desired improvement in anti-knock characteristics and susceptibility to T. E. L. and oxidation inhibitors obtained by my improved process will not result from either of these proc- .ess steps alone but these combined advantages are readily obtained by the correlated steps of my process when carried out under properly controlled conditions.

The distillate from the first stage of my process is not impaired as to the properties just mentioned but also it is not completely nor suillciently sweetened. To effect the desired sweetening, it is essential that the residual, objectionable sulphur compounds be eliminated from the oil, and, according to my improved process, this elimination of residual, objectionable sulphur compounds is accomplished without sacrifice of the advantages obtained by the first stage of the process with respect to these other desirable properties.

I have found that theseladvantages are not 'l5 obtained when air or other oxygen-containing gas is present in the nrst stage of the treatment. Accordingly, a further essentialof my improved process is the rigid exclusion of airfrom the first stage of the process. Further, in order to obtain the maximum benefit with respect to anti-knock characteristics and susceptibility to T. E. L. and oxidation inhibitors, the proper concentration of lead sulphide or blackstrap and air must be maintained in the second stage of the treatment. Where air is present in the first stage of the process or where excessive amounts of air or low concentration of blackstrap are used in the second stage, the advantages of the present invention are materially or wholly lost.

In general, the ilrst stage of the'treatment, in accordance with my invention, comprises the intimate admixing of the sour distillate, devoid of oxygen, with the aqueous caustic solution at an elevated temperature. This treatment is with advantage carried out at a temperature within the range of about 180 to about 260 F., and under sumcient pressure to maintain the distillate in liquid phase. 'I'he concentration of the caustic solution is with advantage about 10 to about 30 B. The mixing may be accomplished by passing the distillate and caustic solution through a conventional mixing device and from thence into an enlarged chamber or tower or by flowing the distillate and caustic solution in countercurrent relation through such chamber or tower. Preferably, the temperature of the distillate is adjusted to the desired range prior to admixing with the caustic solution and the caustic solution is with advantage also at an elevated temperature, say about that of the distillate. It is desirable that the chamber or tower be of considerable volume and cross-sectional area so as'to assure thorough and sufficient time of contact between the caustic solution and the distillate and permit the fouled caustic solution to settle out from the distillate in the lower portion of the chamber. Un-

der such conditions, the former may be Withdrawn from the upper part of the chamber and the fouled caustic solution from the bottom thereof. Preferably a substantial body of caustic solution. is maintained Within the chamber. Air is rigidly excluded from the system.

The partially sweetened distillate from which the caustic solution has been separated is then passed to the second stage of the process wherein it is contacted at an elevated temperature with the lead sulphide suspension or slurry in the presence of a controlled quantity of air. Thereafterthe lead sulphide suspension is separated from the sweet distillate as by settling. As previously noted, the sulphide suspension may be supplied from a doctor sweetening process. The temperature of this second stage of the process is with advantage maintained within the range of about 180 to about 260 F.

Satisfactory results have been obtained using in the first stage of the process caustic soda solution of the concentration previously indicated in amounts approximating 25 to 35 volumes of vcaustic solution for each 100 Volumes of the distillate and approximately the same ratio of the sulphide suspension or slurry to distillate in the second stage. For optimum results, a lead sulphide concentration in excess of 10 pounds per barrel of the caustic-sulphide suspension is required. The air requirement of the second stage is approximately cubic feet Iper thousand barrels of distillate per milligram of mercaptan sulphur per c. c. of distillate.

The process of my present inventionwill l be further deSClibed Bnd illustrated w'ith''efeepe to the speciilc method of operation graphically represented by the now sheet constituting the accompanying drawing. In this method'of operation, the raw distillate which, for instance.A infay 'be stabilizer .ordebutanizer bottoms devoid of'a'ir tionally indicated at 3. The mixer may, with advantage, consist of a series of oriilce plate mixers, and in this the distillate and caustic solution are intimately admixed. From the mixer `tlie admixed distillate and caustic solution pass through line 4 into the chamber 5 which-on theiiow'shee is designated "Caustic treating tower.

'I'he mixture is preferably introduced into the lower partof the tower at a point spaced from the bottom so as to provide a. relatively quiescent zone at the bottom of the tower to facilitate the separation of the distillate from the fouled caustic solution. The mixture may be introduced into the tower as indicated orwith advantage through a spray head (not shown). `Within this tower the distillate is vseparated from the caustic solution by gravity and passed from the topof the tower through thelne 6.

. In the operation of the caustic treating tower, as just described, the admixed caustic solution and sour distillate flow generally concurrently through the tower, spent caustic solution settling out in the bottom of the tower. An alternative arrangement, which may be `used 'with advantage, is to pass the raw distillate unmixed with caustic solution directly into the lower portion of the tower and introduce the caustic solution into the upper portion of the towersotliat they pass through the tower in intimate contact and in a generally countercurrent direction,

lilhis alternative method of operation "may Vbe carried out in the apparatus diagrammatically represented in the drawing by closing they valve enter the apparatus during this stage of the operation. Pressure is maintained on the system suiliciently to maintain the distillate in liquid phase and the temperature, concentration of caustic solution and ratio of caustic solution to distillate are maintained as previously directed. The distillate passing from the upper end of the chamber Yl through line is only partially sweetened and usually contains a considerable proportion of mercaptans, probably as sodium mercaptides. f

As this partially sweetened distillate passes under pressure from the first stage of the operation through line l to the second stage of the operation, there is injected into it a controlled amountof air from line 9 and a suspension or slurry of lead sulphide in caustic solution through lirie Il. The admixture' of distillate, lead sulphide slurry and air are then passed through the mixer I I, which may with advantage be of the type previously described, and into the settling cham- I2 which on the ilow sheet is designated "S'ettler' The'air entering this second stage of the opration will, of course, be under pressure and may be supplied from any convenient source.

In starting up the operation, the caustic-lead sulphide suspension may be supplied from any convenient source through line I3, for instance from a doctor .sweetening process such as 'prevlously noted. However, as the operation progresses, the lead'sulphide suspension thus introduced accumulates in the bottom of the settler I2, and may be circulated therefrom by means of pump Il through lines I4 land I0 back to the stream of distillate passing to the mixer Il. When a suiliciert amount of the lead sulphide suspension has collected in the system, the introduction of llead sulphide suspension through the pipe I3 may be discontinued, the valve there- 40 in closed and the slurry accumulating in the settier I2 continuously circulated through lines I4 and I0 by means of pump I5. -Where desirable,

in line 2 nearest the juncture with line I and pass ing the solution directly into the upper part of `the tower through line 2. With this 'arrangement, the raw distillate may be by-passed around the mixer 3 through line l' by the proper adjustment of the valves shown andv from thence directly into the lower portion of the tower through line 4 without previous mixing of the conventionally indicated on the drawing at 1, the level preferably being maintained-'near the upper end of the chamber-as indicated. 1

The fouled caustic solution which 'separates from the distillate in the chamber 5 is withdrawn therefrom through line l t0 a conventional regenerating system.

The above-described treatin' t of the raw distillate with caustic solution constitutesv the nrst stage of'my process. The raw distillate passing to this-first stage of the process is free from air or oxygen and no air or oxygen is permitted to Vlead sulphide slurry may be withdrawn from the 'system through the valved connection I8.

The lead sulphide appears to act as a catalyst in the oxidation yof the mercaptides as indicated in the preceding Equation C. Lead mercaptides introduced into the system from extraneous sources such as together with the lead sulphide suspension, or formed during -the operation, are oxidized to lead oxide as indicated in previous 'Equation D. Hydrogen sulphide may be injected into the system through valved connection I8,

as required, to `convert such lead .oxide to lead sulphide'so as to assist in establishing and to maintain the proper concentration of lead sulphideinthe System.

Settler I2 is with advantage of such size and 'shape as to permit adequate settling and sep-arationV of the blackstrap from the. distillate and, for

this samereason; it is desirable to maintain considerable volume of the slurry-distillate mixture "storage Where the herein-prescribed processing conditions, including 'particularly' temperatures, concentrations and requirements as to air, are prop- 'erly ycont--olled and regulated in the respective successive stages of the treatment, as-herein directed, there is obtained from the second stage of my process a doctor sweet distillate having improved anti-knock characteristics and susceptibility to T. E. L. and oxidation inhibitors. Advantageously, this second step of my process is carried out at a temperature within the range of about 180 F. to about 260 F. and, though the optimum proportion of air and proportion and concentration of lead sulphide vary somewhat with the particular distillate treated, proportions and concentrations approximating those previously indicated have been found to give generally satisfactory results.

The advantages of my improved sweetening process with respect to octane number and susceptibility to improvement by T. E. L., is illustrated by the following specific examples wherein the first stage of the operation was carried out at a temperature of 200 F. and one volume of 25 B. caustic solution was used for each three volumes of distillate, the operation being carried out under a pressure of 30 pounds per square inch and the operating rate being such that the distillate was in intimate contact with the caustic solution under this pressure for about 15 minutes. In these operations the charge was a stabilized cracked distillate, i. e. mixed debutanizer bottoms, free from air and having an initial boiling point of 116 F. and an end point of 400 F. iAir was carefully excluded from the operations.

In two illustrative runs. the characteristics of the feed stock and of the partially sweetened distillate from the first stage of the operation, in the respective runs, were as follows:

Run l Run 2 From From Feed Feed lst stage stage Gravity, A. P. I 58.9 58. 7 58.6 5S. 6 Reid vapor pressure at 100 F 5. 3 5. 2 5. 5 5.5 Mercaptan sulphur, mas/100e. c 23. 4 7. 6 23. 4 7. 4 Mercaptan sulphur, reductmn,

percent 67. 5 68. 4 Octane number (motor method):

Neat 61. 1 6l. 3 60. 3 61. 3 68. 5 68. 7 68.0 69. 3 70. 8 71` 9 70. 4 72. 2 +3 c. c. T. E. L 73. 4 73. 7 73.0 73.8

As appears from the foregoing tabulation, the octane number of the partially sweetened distillate from the first stage of my process was in each instance increased by the treatment. This is true of the neat distillate and also of the distillate to which various proportions of T. E. L. were added, indicating a material improvement with respect to anti-knock characteristics.

However, this partially-treated distillate still contained a substantial proportion of mercaptan sulphur which must be removed in order to obtain a doctor-sweet distillate. The complete removal of the mercaptan sulphur without depreciation of the distillate with respect to anti-knock characteristics or susceptibility to T. E. L. or anti-oxidants is accomplished by my improved two-stage process by subjecting the partially sweetened distillate from the first stageof treatment to the second stage and therein, at a temperature of about 200 F., admixing it with approximately 25% by volume of blackstrap suspension containing in excess of 10 pounds of lead sulphide per barrel of the suspension and approximately 57 cubic feet of air per 100 barrels of distillate in run 1 and about 55.5 cubic feet of air per 100 barrels of distillate in run 2.

The characteristics of the distillate from the assigns Accordingly, it appears that by my improved two-step process, the mercaptan sulphur may be completely eliminated and a doctor sweet distillate obtained not only without sacrifice of antiknock characteristics but, in many instances, with materially improved characteristics with respect thereto.

I claim:

1. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about 180 F. to 260 F. and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B., separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 F., and in the presence of a controlled quantity of air, with a suspension of lead sulphide in aqueous caustic solution.

2. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at an elevated temperature and in the absence of air, with an aqueous solution of caustic soda, separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at an elevated temperature and in the presence of a controlled quantity of air, with a suspension of lead sulphide in aqueous caustic solution.

`3. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately -contacting the distillate, at a temperature of about 180 F. to 260 F. and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B., separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 F., and, in the presence of a controlled quantity of air equivalent to approximately 75 cubic feet of air per thousand barrels of distillate per milligram of mercaptan sulphur per c.c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution.

4. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about F. to 260 F., and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B., separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 F., and in the presence of a controlled quantity of air equivalent to approximately 75 cubic feet of air per thousand Ibarrels of distillate .per milligram of mercaptain sulphur per 100 c.c. of the distillate, with a suspension oi.' lead sulphide in aqueous caustic solution comprising not less than about pounds of the sulphide per barrel of the suspension. l

5. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about 180 F. to 260 F. and in the absence of air, with an aqueous solution of I'caustic soda of 10 to 30 B., separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 F. and in the presence of a controlled quantity of air equivalent to approximately 75 cubic feet of air per thousand barrels of distillate lper milligram of mercaptan sulphur per 100 c.c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution comprising not less than about 10 pounds of the sulphide per barrel of the suspension and in proportions of about 25 to 35 volumes of thel caustic-lead sulphide suspension for each 100 volumes of distillate.

6. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about 180 F. to 260 F. and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B. in proportions of about 25 to 35 volumes of caustic solution for each 100 volumes of distillate, 'separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 Fand in the presence of a controlled quantity of air equivalent to approximately 75 cubic feet of air per thousand barrels of distillate per milligram of mercaptan sulphur per 100 c. c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution.

'7. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about 180 F. to 260 F. and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B. in proportions of about 25 to 35 volumes of caustic solution for each 100 volumes of distillate, separating the distillate from the fouled caustic solution and intimately contacting the separated distillate, at a temperature of about 180 F. to 260 F. and in the presence of a controlled quantity of air equivalent to approximately cubic feet of air per thousand barrels of distillate per milligram of mercaptan sulphur per c. c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution comprising not less than about 10 pounds of the sulphide per barrel of the suspension.

8. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about F. to 260 F. and in the absence of air, with an aqueous solution of caustic soda of 10 to 30 B., in proportions of about 25 to 35 Volumes of caustic solution for each 100 volumes of distillate, separating the distillate from the fouled' caustic solution and intimately contacting the separated distillate, at a, temperature of about 180 F. to 260 F.. and in the presence of a controlled quantity of air equivalent to approximately 75 cubic feet of air perthousand barrels of distillate per milligram of mercaptan sulphur per 100 c. c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution comprising not less than about 10 pounds of the sulphide per barrel of suspension and in proportions of about 25 to 35 volumes of the caustic-lead sulphide suspension for each 100 Volumes of distillate.

9. A process for the treatment of light petroleum distillate containing undesirable sulphur compounds to eliminate said sulphur compounds therefrom comprising intimately contacting the distillate, at a temperature of about 200 F. and in the absence `of air, with an aqueous solution of caustic soda of about 25 B. in proportions of vabout one volume of caustic solution for each three volumes of distillate, separating the distillate from the fouled caustic solution and intimately contactingv the separated distillate, at a temperature of about 200 F. and in the presence ofra controlled quantity of air equivalent izo-approximately 75 cubic feet of air per thousand barrels of distillate per milligram of mercaptan sulphur per 100 c. c. of the distillate, with a suspension of lead sulphide in aqueous caustic solution comprising not less than about 10 pounds of the sulphidev per barrel of suspension and in proportions of about 25 to 35 volumes of the caustic-lead sulphide suspensionfor each 100 volumes of distillate.

FRANK A. APGAR. 

